ScienceDaily (Aug. 30, 2010) — Computational scientistsand geophysicists at the University of Texas at Austin and the CaliforniaInstitute of Technology (Caltech) have developed new computer algorithms thatfor the first time allow for the simultaneous modeling of Earth's mantle flow,large-scale tectonic plate motions, and the behavior of individual fault zones,to produce an unprecedented view of plate tectonics and the forces that driveit.
A paper describing the whole-earth model and itsunderlying algorithms will be published in the August 27 issue of the journalScience and also featured on the cover. 一篇作為封面將刊載于八月份第27期科學(xué)雜志的論文將描述這個全地球模型及其基層算法。 The work "illustrates the interplay between makingimportant advances in science and pushing the envelope of computationalscience," says Michael Gurnis, the John E. and Hazel S. Smits Professor ofGeophysics, director of the Caltech Seismological Laboratory, and a coauthor ofthe Science paper. 這項工作將“舉例說明在利用科學(xué)給出重要建議和增強(qiáng)計算機(jī)科學(xué)方面的能力之間的相互影響”，麥克爾·格尼斯，地球物理學(xué)教授，加州理工地震學(xué)實驗室主任，科學(xué)雜志論文的合著者約翰·E與黑茲爾·S·斯密斯說道。 To create the new model, computational scientists atTexas's Institute for Computational Engineering and Sciences (ICES) -- a teamthat included Omar Ghattas, the John A. and Katherine G. Jackson Chair inComputational Geosciences and professor of geological sciences and mechanical engineering,and research associates Georg Stadler and Carsten Burstedde -- pushed theenvelope of a computational technique known as Adaptive Mesh Refinement (AMR). 為建立這個新模型，德克薩斯計算機(jī)工程與科學(xué)學(xué)院（ICES)的計算機(jī)科學(xué)家們 —— 一個包括奧馬爾·伽特斯，計算機(jī)地球科學(xué)系主任，地質(zhì)學(xué)和機(jī)械工程學(xué)教授約翰·A同凱瑟琳·G·杰克森，以及研究合伙人格奧爾格·斯泰德勒和卡斯滕·布斯特德 —— 增強(qiáng)被稱為自適應(yīng)精細(xì)網(wǎng)格的計算機(jī)技術(shù)系統(tǒng)的運(yùn)行能力 Partial differential equations such as those describingmantle flow are solved by subdividing the region of interest (such as themantle) into a computational grid. Ordinarily, the resolution is kept the samethroughout the grid. However, many problems feature small-scale dynamics thatare found only in limited regions. "AMR methods adaptively create finer resolutiononly where it's needed," explains Ghattas. "This leads to hugereductions in the number of grid points, making possible simulations that werepreviously out of reach." 像用于描述地幔流的偏微分方程就通過將感興趣的區(qū)域（例如地幔）細(xì)分到計算機(jī)網(wǎng)格中被解答。一般，網(wǎng)格的解析率是均一的。但是，很多問題針對只建立在有限區(qū)域內(nèi)的小規(guī)模動力學(xué)?！?span>AMR方法僅在需要的地方自適應(yīng)性的使用更高的解析率，”伽特斯解釋道?！斑@導(dǎo)致格點數(shù)量大幅減少，使得原先超出研究范圍的仿真成為可能?！?/span> "The complexity of managing adaptivity amongthousands of processors, however, has meant that current AMR algorithms havenot scaled well on modern petascale supercomputers," he adds. Petascalecomputers are capable of one million billion operations per second. To overcomethis long-standing problem, the group developed new algorithms that, Bursteddesays, "allows for adaptivity in a way that scales to the hundreds ofthousands of processor cores of the largest supercomputers availabletoday." “然而，管理數(shù)千處理器之間的自適應(yīng)分配的復(fù)雜性，意味著目前的AMR算 法不能很好的在現(xiàn)代千萬億次超級計算機(jī)上按比例分配任務(wù)，”他補(bǔ)充道。千萬億次計算機(jī)能夠每秒鐘運(yùn)算一千萬億次。為了解決這個長期存在的問題，這個團(tuán)隊開 發(fā)了新的算法，它“允許某種程度上使得在最大的超級計算機(jī)上自適應(yīng)性的按比例分配任務(wù)給數(shù)十萬處理器成為可能?！辈妓固氐抡f道。 With the new algorithms, the scientists were able tosimulate global mantle flow and how it manifests as plate tectonics and themotion of individual faults. According to Stadler, the AMR algorithms reducedthe size of the simulations by a factor of 5,000, permitting them to fit onfewer than 10,000 processors and run overnight on the Ranger supercomputer atthe National Science Foundation (NSF)-supported Texas Advanced Computing Center. 使用新算法，科學(xué)家們能夠模擬全球地幔流動以及它是如何顯明板塊構(gòu)造和斷層移動的。據(jù)斯泰德勒說，AMR算法通過5千個要素減小仿真尺寸，允許它們在國家科學(xué)基金的空閑超級計算機(jī)—由德克薩斯先進(jìn)計算機(jī)中心維護(hù)，上用少于1萬個處理器通宵運(yùn)行。 A key to the model was the incorporation of data on amultitude of scales. "Many natural processes display a multitude ofphenomena on a wide range of scales, from small to large," Gurnisexplains. For example, at the largest scale -- that of the whole earth -- themovement of the surface tectonic plates is a manifestation of a giant heatengine, driven by the convection of the mantle below. The boundaries betweenthe plates, however, are composed of many hundreds to thousands of individualfaults, which together constitute active fault zones. "The individualfault zones play a critical role in how the whole planet works," he says, "andif you can't simulate the fault zones, you can't simulate plate movement"-- and, in turn, you can't simulate the dynamics of the whole planet. 模型的關(guān)鍵在于超大尺寸上的數(shù)據(jù)結(jié)合?！昂芏嘧匀贿^程在一個寬泛的尺寸上顯示大量的現(xiàn)象，從微觀到宏觀，”格尼斯解釋道。例如，在最大的尺寸上—整個地球—表面構(gòu)造板塊的移動表現(xiàn)為一個由地幔流的熱循環(huán)驅(qū)動的巨型熱力發(fā)動機(jī)。然而，板塊間的邊界由無數(shù)獨立斷層組成，它們一起組成斷層區(qū)域?！蔼毩鄬訁^(qū)域在整個板塊如何工作上扮演著重要角色，”他說，“如果你不能模擬斷層區(qū)域，你就不能模擬板塊運(yùn)動”--其次，你就不能模擬整個板塊的動態(tài)。 In the new model, the researchers were able to resolvethe largest fault zones, creating a mesh with a resolution of about onekilometer near the plate boundaries. Included in the simulation wereseismological data as well as data pertaining to the temperature of the rocks,their density, and their viscosity -- or how strong or weak the rocks are,which affects how easily they deform. That deformation is nonlinear -- withsimple changes producing unexpected and complex effects. 在新的模型里，研究人員能夠分解最大的斷層區(qū)域，在接近板塊邊緣處創(chuàng)建一個分辨率大約一公里的網(wǎng)絡(luò)。模擬包括地震學(xué)數(shù)據(jù)還有巖石的溫度，密度，粘性--或者這些巖石有多堅硬或柔軟這類影響它們有多容易變形的固有數(shù)據(jù)。這些變形是非線性的--簡單的改變也會產(chǎn)生出乎預(yù)料和復(fù)雜的影響。 "Normally, when you hit a baseball with a bat, theproperties of the bat don't change -- it won't turn to Silly Putty. In theearth, the properties do change, which creates an exciting computationalproblem," says Gurnis. "If the system is too nonlinear, the earthbecomes too mushy; if it's not nonlinear enough, plates won't move. We need tohit the 'sweet spot.'" “平常，當(dāng)你用球棒擊球時，球棒的屬性不會發(fā)生變化—它不會變成橡皮泥。在地球模型上，屬性會發(fā)生變化，這種變化產(chǎn)生一個令人激動的計算問題，”格尼斯說。“如果系統(tǒng)過于非線性，這個地球會變得太軟；如果不夠非線性，板塊將不會運(yùn)動。我們需要正好打倒‘擊球點’上。 After crunching through the data for 100,000 hours ofprocessing time per run, the model returned an estimate of the motion of bothlarge tectonic plates and smaller microplates -- including their speed anddirection. The results were remarkably close to observed plate movements. 在以每次運(yùn)行用十萬小時處理時間對數(shù)據(jù)進(jìn)行處理后，模型反饋一個大型結(jié)構(gòu)板塊與較小的微型板塊兩者的運(yùn)動的估計值。計算結(jié)果與觀測到的板塊運(yùn)動非常接近。 In fact, the investigators discovered that anomalousrapid motion of microplates emerged from the global simulations. "In thewestern Pacific," Gurnis says, "we have some of the most rapidtectonic motions seen anywhere on Earth, in a process called 'trench rollback.'For the first time, we found that these small-scale tectonic motions emergedfrom the global models, opening a new frontier in geophysics." 事實上，調(diào)查人員從地球模擬器中發(fā)現(xiàn)微型板塊不尋常的快速移動?！霸谖魈窖螅备衲崴拐f，“我們獲得了在地球某些地方發(fā)現(xiàn)的大量快速結(jié)構(gòu)移動中的幾處，這一過程被稱為‘海溝反轉(zhuǎn)’。我們首次發(fā)現(xiàn)這樣一些小規(guī)模結(jié)構(gòu)運(yùn)動從地球模型中浮現(xiàn)出來，它們在地球物理領(lǐng)域開創(chuàng)了一個新前沿。 One surprising result from the model relates to theenergy released from plates in earthquake zones. "It had been thought thatthe majority of energy associated with plate tectonics is released when platesbend, but it turns out that's much less important than previouslythought," Gurnis says. "Instead, we found that much of the energydissipation occurs in the earth's deep interior. We never saw this when welooked on smaller scales." 一 個來自地球模型的令人意外的成果涉及到地震區(qū)域里自板塊釋放的能量?！澳芰康拇蟛糠衷徽J(rèn)為與板塊彎曲時板塊結(jié)構(gòu)被釋放的過程有關(guān)，然而結(jié)果顯示其并沒有 原先想象得那么重要?！霸谶@之外，我們發(fā)現(xiàn)多數(shù)能量耗散發(fā)生在地球內(nèi)部深處。這是在我們觀察更小規(guī)模的模型時無法看到的?！?/span> |
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